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Molecular formulas

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Molecular formulas Review of Moles Avogadros number 6.022 x 1023 Particles per mole of a substance The particles can be atoms, molecules or ions Molar Mass The mass ... – PowerPoint PPT presentation

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Title: Molecular formulas


1
Molecular formulas

2
Review of Moles
  • Avogadros number
  • 6.022 x 1023 Particles per mole of a substance
  • The particles can be atoms, molecules or ions
  • Molar Mass
  • The mass of one mole of a substance

3
Review Average Atomic Mass
  • weighted average of the atomic mass of an
    elements isotopes
  • Found by
  • taking into account the abundance of an atom in
    the environment

4
Formula Mass link
  • Formulas for covalent compounds show the elements
    and the number of atoms of each element in a
    molecule.
  • Formulas for ionic compounds show the simplest
    ratio of cations and anions in any pure sample.

5
Empirical vs actual vs molecular formulas
  • empirical formula
  • shows the simplest ratio for the relative numbers
    and kinds of atoms in a compound.
  • ammonium nitrate is NH2O
  • actual formula
  • shows the actual ratio of elements or ions in a
    single unit of a compound.
  • NH4NO2
  • molecular formula
  • is a whole-number multiple of the empirical
    formula

6

7
Determining Empirical Formulas
  • You can use the percentage composition for a
    compound to determine its empirical formula.
  • Convert the percentage of each element to g.
  • Convert from g to mol using the molar mass of
    each element as a conversion factor.
  • Compare these amounts in mol to find the simplest
    whole-number ratio among the elements.

8
Determining an Empirical Formula from Percentage
Composition
Sample Problem G Chemical analysis of a liquid
shows that it is 60.0 C, 13.4 H, and 26.6 O by
mass. Calculate the empirical formula of this
substance. link
9
Determining an Empirical Formula from Percentage
Composition
Sample Problem G Solution Assume that you have a
100.0 g sample, and convert the percentages to
grams. for C 60.0 ? 100.0 g 60.0 g C for
H 13.4 ? 100.0 g 13.4 g H for O 26.6 ?
100.0 g 26.6 g O
10
Determining an Empirical Formula from Percentage
Composition
Sample Problem G Solution, continued Convert the
mass of each element into the amount in moles,
using the molar mass.
11
Determining an Empirical Formula from Percentage
Composition
Sample Problem G Solution, continued The formula
can be written as C5H13.3O1.66, but you divide by
the smallest subscript to get whole numbers.
The empirical formula is C3H8O.
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